In recent years, it has been desired to increase a storage capacity of a magnetic disk drive that is used as an external recording device for an information processing device such as a computer. In addition, it has been desired to reduce the size of the magnetic disk drive. To meet those needs, it has been required to further increase a recording density of the magnetic disk drive. Thus, a perpendicular recording scheme has become a mainstream instead of a conventional longitudinal recording scheme. In the perpendicular recording scheme, it is easier to record data at high density.
In the perpendicular magnetic recording scheme, at least a perpendicular recording medium and a perpendicular magnetic recording head are used. The perpendicular recording medium has anisotropy in a direction perpendicular to the surface of a film thereof. The perpendicular magnetic recording head is functional to effectively apply a magnetic field in a direction perpendicular to the surface of the medium. The perpendicular magnetic recording head includes of at least a coil conductor and a magnetic circuit. The magnetic circuit is interlinked with the coil conductor. The magnetic circuit typically includes of an auxiliary pole and a main pole. Due to flow of a recording current with a polarity corresponding to an electrical signal in the coil conductor, a recording magnetic field corresponding to the current polarity is generated from the main pole. The main pole faces the recording medium and magnetizes a recording layer of the medium. In this case, the recording layer is located immediately under the recording medium. A change in a polarity of the recording magnetic field is recorded as a change in the direction of the magnetization of the recording medium. A soft magnetic underlayer is provided under the recording layer constituting a part of the perpendicular recording medium. The soft magnetic underlayer has a function of returning a magnetic flux acting on the recording layer to the auxiliary pole. In order to efficiently achieve this function, the area of a surface (facing the recording medium) of the auxiliary pole is larger than the area of a surface (facing the recording medium) of the main pole. Magnetic information is recorded by changing the direction of the magnetization of the perpendicular recording medium by means of those functions.
In the perpendicular recording scheme, high-density magnetic information (presence of differently magnetized regions) is recorded. Thus, it is desirable to further reduce the width (that determines the limit of the recording density) of a magnetic transition region located between adjacent regions magnetized in respective opposite directions.
It is widely known that the width of the magnetic transition region is affected by the gradient of the magnetic field produced by the perpendicular magnetic recording head. Japanese Patent Office (JPO) Pub. No. JP-A-2004-310968 discloses a perpendicular magnetic recording head having a main pole and a soft magnetic film provided next to the main pole in a track width direction in order to increase the gradient of a magnetic field produced by the magnetic recording head. JPO Pub. No. JP-A-2005-18851 discloses a perpendicular magnetic recording head having a main pole and a soft magnetic film. The soft magnetic film disclosed in JPO Pub. No. JP-A-2005-18851 is provided on a trailing side of the main pole to cause the gradient of a magnetic field produced by the magnetic recording head to be steep. JPO Pub. No. JP-A-2005-190518 and JPO Pub. No. JP-A-2007-35082 each disclose a structure of a recording head, in which a magnetic shield film surrounds a main pole. JPO Pub. No. JP-A-2007-294059 discloses a structure of a perpendicular magnetic recording head, in which a distance (side gap length) between a main pole and each of magnetic side shields varies depending on the position in a depth direction of a perpendicular magnetic recording head from an air bearing surface. The magnetic side shields arranged on both sides of the main pole are adapted to prevent a magnetic field from leaking toward adjacent tracks. A magnetic shield placed on a trailing side (upper side) of the main pole is adapted to increase the gradient of a magnetic field produced by the magnetic recording head.
In the aforementioned conventional techniques, the soft magnetic films surround the main pole. The soft magnetic films arranged on both sides of the main pole can prevent the magnetic field from leaking toward the adjacent tracks, while the soft magnetic film located on the trailing side (upper side) of the main pole can increase the gradient of the magnetic field. Therefore, data can be recorded in a narrow data track in the aforementioned conventional techniques. However, the intensity of the magnetic field may be reduced, or data may be recorded on an adjacent track due to the shield film(s), depending on the thicknesses of the soft magnetic films or on a combination of saturation magnetic flux densities. Those problems have prevented data from being recorded in a narrow track.
In view of the aforementioned problems, it would be desirable to provide a high-performance perpendicular magnetic recording head and a method for manufacturing the perpendicular magnetic recording head.